Comment by cromulent

To illustrate the difference (hopefully I get this right): A transaction needs to balance, left vs right.

For example, you receive a sales order for 1000€ of widgets, which cost you 600€. You ship them. You invoice for 1000€.

No money moved (hopefully you do get paid at some point though). However, you need to do some bookkeeping.

On the left side of the ledger (debits): Accounts receivable 1000€. Cost of goods sold 600€.

On the right side of the ledger (credits): Revenue goes up by 1000€. Inventory goes down by 600€.

These completely match. No money has moved, but the books are now up to date and balance.

Any transaction that does not balance should be rejected.